This invention relates to the recovery of iron values which would otherwise be lost as constituents of a waste slag.
While it has long been known that substantial quantities of iron have been lost through the discarding of slags (e.g., copper smelter slags), the lack of an economical recovery process, as compared to other sources of iron, has prevented the commercial acceptance of iron recovery from such slags. Furthermore, despite a substantial rise in the price of iron in recent years and despite the transportation costs involved in transporting iron to the location of a copper smelter to fulfill the need for iron in various processes (see, for example, U.S. Pat. No. 3,232,742, issued Feb. 1, 1966, and owned by the Assignee of the present invention), recovery of iron from copper smelting slags has evidently been ignored because of the lack of a suitable process.
As explained in U.S. Pat. Nos. 3,857,699 and 3,857,700 (both issued Dec. 31, 1974, owned by the Assignee of the present invention, and incorporated herein by reference), highly oxidized copper smelter slags can be treated to recover copper and molybdenum values therefrom. According to the present invention, however, it has been discovered that the slag remaining after the recovery of these metal values, which formed a waste product in those patents, can itself be treated to make feasible the recovery of iron from that slag.
Of course, it has long been known that ferrous silicates in slags can be reduced using carbon in order to recover iron from the slag. Examples of the many references acknowledging this theoretical possibility are Bryk et al., U.S. Pat. No. 2,523,092; Edlund, "Smelting Copper Reverberatory Slags to Recover Iron of Low Copper and Sulfur Content", Bureau of Mines Report of Investigations 6481 (1964); and Zimmerley et al, U.S. Pat. No. 3,232,742. In none of these references, however, is there any suggestion of the slag composition, and reaction rate enhancement technique, which have been identified according to the present invention as crucial to a commercially feasible recovery of iron from slags.
In view of the foregoing, it is a principle object of the present invention to provide an improved technique for recovery of iron from slag.